You can look up Marty's website where he has a multi-camera editing tutorial. But here is how I do it:
Track 1 - Master video track
Track 2 - Camera 1
Track 3 - Camera 2
First, you have to sync tracks 2 and 3. Then, I can solo tracks 2 or 3 to see the individual cameras. Wherever I want to change cameras, I just CTRL-A and S (select all and split), then click on the segment and use the numpad 8 key to move it up to the master track. If I want dissolves between the segments, I then get on the split on the master track and press the numpad / key to convert the cut to a dissolve.
Multi-camera editing is really very easy with Vegas.
If you don't want to do splits/cuts as enumerated above, you can add compositing lines on master and track 2 at the same time, use the opacity to drive the cuts/dissolves. Makes it rock n' rollin' fast!
Right-click the track header, choose Insert/Remove Envelope and then choose Composite Level. You will then have to add nodes as needed to fade out the top track so the lower track can be seen and then fade back to the top track.